The present invention relates to flat rolled metal and sheet metal processing. More particularly, the present invention relates to a method and apparatus for leveling and conditioning sheet metal using a tension-leveling machine in combination with a surface conditioning system.
A wide variety of manufactured goods contain processed sheet metal. For example, aircraft, automobiles, file cabinets and household appliances, to name only a few, contain sheet metal. The sheet metal is typically purchased directly from steel mills and/or steel service centers, but may be passed through intermediate processors (sometimes referred to as xe2x80x9ctollxe2x80x9d processors) before it is received by an original equipment manufacturer.
Various methods exist for flattening sheet metal and for conditioning the surfaces thereof. Flatness of sheet metal is important because virtually all stamping and blanking operations require a flat sheet. Also, in certain applications, such as in the aerospace industry, residual stress free material is critical. Good surface conditions are also important, especially in applications where the top and/or bottom surfaces of the metal sheet will be painted.
There are a number of common defects that effect sheet metal flatness. For example, when sheet metal is rolled into coil form for convenient storage and transportation, the strip takes on a coiled shape. This curvature is commonly referred to as xe2x80x9ccoil set.xe2x80x9d Coil set occurs because the sheet metal has been bent past its yield point. More specifically, when sheet metal is coiled, the metal fibers near the inside surface of the curved sheet are compressed past their yield point, and the metal fibers near the outside surface of the curved sheet are stretched past their yield point. Another type of shape defect known as xe2x80x9cedge wavexe2x80x9d occurs if the edge portions of the sheet are longer than the center portion of the sheet, resulting in undulations in one or both of the edge portions of the sheet. A similar type of shape defect known as xe2x80x9ccenter bucklexe2x80x9d results if the center portion of the sheet is longer than one or both of the edge portions, which results in bulging or undulating of the central portion of the sheet.
One proven method of leveling sheet metal is tension leveling. In general, a conventional tension leveling apparatus comprises a drag bridle, a pull bridle downstream from the drag bridle, and a tension leveler between the drag bridle and pull bridle. The drag and pull bridles each include a plurality of rollers that rotate to advance the metal sheet therethrough. The tension leveler located between the drag and pull bridles includes a plurality of smaller radius leveling rollers that are offset from one another to impart bending stresses in the metal sheet as the sheet is advanced therethrough. In operation, the metal sheet is unwound from an upstream xe2x80x9cpay-offxe2x80x9d reel and threaded through the aforementioned components of the tension leveling apparatus. Rollers of the pull bridle turn slightly faster than rollers of the drag bridle, so that the metal sheet is placed in substantial tension between the pull and drag bridles, while the metal sheet is passing through the leveling rollers. This tension is preferably sufficient to stretch all fibers in the metal sheet side-to-side and top-to-bottom. The effect of this tension is to cause all parts of the metal sheet between the drag and pull bridles, including the center fibers of the sheet, to exceed the material yield point as the metal sheet is made to conform to the smaller radius of the leveling rollers located between the drag and pull bridles. Tension levelers are also advantageous because, in general, they are faster than other types of leveling machines, such as stretcher levelers. Typically, tension levelers can handle between 150 and 1,500 linear feet of metal sheet per minute, depending on the gauge of the metal sheet (i.e., for heavier gauge, the linear speed will generally be lower than for lighter gauge), and typically as much as 72xe2x80x3 in width. While such tension levelers have proven to be effective in leveling sheet metal, even in a coil-to-coil operation, a tension leveling apparatus alone does nothing to improve the surface quality of the sheet metal.
Thus, there is a need for a sheet metal processing apparatus that incorporates the benefits of a tension leveler together with a surface conditioning apparatus that removes scale and other smut from the surface in a continuous strip of sheet metal.
It is a principal object of the present invention to provide a method and apparatus for processing sheet metal which benefits from the synergy of combining a tension-leveling machine and an adjacent surface conditioner, whereby the performance of the surface conditioner is improved at least in part due to its location relative to the various components of the tension-leveling machine, and also due to the fact that the tension leveling is a continuous operation. A related object is to provide a method and apparatus for processing sheet metal that incorporates the benefits of a tension-leveling machine, for flattening the metal sheet and for reducing or eliminating internal residual stresses in the sheet metal, and also incorporates the benefits of a surface conditioning process that employs abrasive, rotating cleaning brushes, which are brought into engagement with the surface of the sheet metal to remove scale and other smut from the surface. Another object of the invention is to provide a sheet metal processing apparatus that incorporates a tension leveler and a surface conditioning process together in-line to reduce material handling costs. Still another object is to provide a metal processing apparatus that is capable of flattening as well as reducing or eliminating internal residual stresses from sheet metal in a coil-to-coil processing operation. A further object of the invention is to provide a sheet metal processing apparatus that is easier and more economical to run than conventional temper mills. Still another object is to provide a metal processing apparatus that is capable of providing superior flatness, even in severely deformed metal coils, and conditioning the surface, thus making the finished product more marketable.
In general, a method of the present invention for processing sheet metal comprises the steps of: providing a tension-leveling apparatus; providing a surface conditioning apparatus; engaging a portion of the sheet metal with the tension-leveling apparatus; and conditioning a surface of the portion of the sheet metal with the surface conditioning apparatus. The tension-leveling apparatus includes a first set of bridle rollers adapted to receive sheet metal from an upstream coil. The tension-leveling apparatus also includes a second set of bridle rollers downstream of the first set of bridle rollers. The tension-leveling apparatus is adapted to engage the sheet metal in a manner to subject the portion of the sheet metal between the first and second sets of bridle rollers to a tensile force that is sufficient to flatten the portion of the metal sheet. The surface conditioning apparatus is located downstream of the first set of bridle rollers. The surface conditioning apparatus has at least one rotating conditioning member. The step of conditioning the surface of the portion of the sheet metal includes bringing the rotating conditioning member into engagement with the surface in a manner to remove scale from the surface.
In another aspect of the present invention, a method of leveling and surface-conditioning sheet metal, in line, in a continuous coil-to-coil processing operation, comprises the steps of: providing a tension-leveling apparatus; providing a surface conditioning apparatus adjacent to the tension-leveling apparatus; advancing a continuous length of sheet metal from an upstream coil through the tension-leveling apparatus; applying a tensile force to a portion of the sheet metal between the first and second sets of bridle rollers; leveling the portion of the sheet metal between the first and second sets of bridle rollers; directing the continuous length of sheet metal through the surface conditioning apparatus; and conditioning a surface of the sheet metal with the surface conditioning apparatus. In this aspect of the invention, the tension-leveling apparatus includes a first set of bridle rollers, a second set of bridle rollers downstream of the first set of bridle rollers, and a set of leveling rollers between the first and second sets of bridle rollers. The step of advancing the continuous length of sheet metal through the tension-leveling apparatus includes advancing the continuous length of sheet metal through the first set of bridle rollers, through the set of leveling rollers and through the second set of bridle rollers. The tensile force applied to the portion of the sheet metal between the first and second sets of bridle rollers is applied continuously to that portion by the first and second sets of bridle rollers as the sheet metal is advanced. The step of leveling the portion of the sheet metal between the first and second sets of bridle rollers is accomplished by bringing the set of leveling rollers into engagement with the sheet metal in a manner so that the portion of the sheet metal is made to conform to the leveling rollers while being subjected to the tensile force. The surface conditioning apparatus is positioned in line with the tension-leveling apparatus and downstream of the first set of bridle rollers. The surface conditioning apparatus has at least one rotating conditioning member. The step of directing the continuous length of sheet metal through the surface conditioning apparatus is performed as the continuous length of sheet metal is advanced through the first and second sets of bridle rollers. The step of conditioning the surface of the sheet metal is accomplished by bringing the rotating conditioning member into engagement with the surface of the sheet metal in a manner to remove scale therefrom.
In still another aspect of the invention, a metal processing apparatus comprises a tension-leveling apparatus and an adjacent surface conditioning apparatus. The tension-leveling apparatus is adapted to receive a continuous length of sheet metal from an upstream coil. The tension-leveling apparatus has a first set of bridle rollers, a second set of bridle rollers downstream of the first set of bridle rollers, and a set of leveling rollers between the first and second sets of bridle rollers, the first and second sets of bridle rollers. The first and second sets of bridle rollers are adapted to engage the sheet metal in a manner to subject a portion of the sheet metal between the first and second sets of bridle rollers to a first tensile force. The set of leveling rollers is adapted to engage the portion of the sheet metal between the first and second sets of bridle rollers in a manner so that the portion is made to conform to surfaces of the leveling rollers while subjected to the tensile force. The surface conditioning apparatus is located downstream of the first set of bridle rollers of the tension-leveling apparatus. The surface conditioning apparatus has at least one rotating conditioning member, which is adapted for engagement with a surface the sheet metal in a manner to remove scale from the surface.
Other objects and features of the invention will be in part apparent and in part pointed out hereinafter. While the principal advantages and features of the present invention have been described above, a more complete and thorough understanding and appreciation for the invention may be attained by referring to the drawings and description of the preferred embodiments, which follow.